The invention relates to a device for determining the concentration of hydrogen in a fluid atmosphere. There is a variety of applications for detecting and monitoring the presence of hydrogen. Examples of detecting hydrogen in gaseous atmospheres include smoke detectors, inert coolant atmospheres in transformers, motors and generators and nuclear reactor containment atmospheric monitors.
An example of detecting hydrogen in a liquid includes the measurement of hydrogen in the liquid sodium of a sodium cooled nuclear reactor as a means for detecting water leakage into the sodium from the sodium-water heat exchanger or steam generator.
A number of hydrogen detection arrangements are known. Diffusion cells, based upon the high permeability of certain materials to hydrogen, have been used to concentrate the hydrogen from an atmosphere and apply it to a pressure sensitive sensor such as an ionization gauge, mass spectrograph, Penning gauge or the like to measure the partial pressure of hydrogen in the sensor. Another approach involves the measurement of hydrogen ions in a non-conducting fluid (e.g. pH meters). Still other devices are known which utilize electrochemical reactions to generate a voltage proportional to the hydrogen concentration, such devices being analogous to fuel cells.
Among prior publications concerning detection of gases are the following:
"Ionization Methods for the Analysis of Gases and Vapors" by J. E. Lovelock, Analytical Chemistry, Vol. 33, No. 2, February 1961, pages 162-177. This paper describes various aspects of ionization types of gas detectors.
U.S. Pat. No. 3,683,272 shows a diffusion membrane and ion pump arrangement particularly adapted for detecting hydrogen in liquid sodium.
U.S. Pat. No. 3,866,460 shows apparatus including a hydrogen diffusion membrane and pressure or combustibility measuring means for detecting hydrogen in the liquid coolant of electrical apparatus.
U.S. Pat. No. 3,927,555 shows a palladium alloy tube which undergoes volumetric change as a function of the hydrogen concentration to which it is exposed. A linear variable differential transformer detects the change in the length of the tube as an indication of the hydrogen concentration.
U.S. Pat. No. 3,977,232 shows a diffusion membrane and ion pump arrangement for measuring the concentration of hydrogen in liquid and gaseous environments.
Despite the numerous hydrogen detector arrangements of the prior art, there remains a need for a hydrogen sensor which is small in size and low in cost, is of simple rugged design with long shelf and operating life, has high sensitivity, fast response, is useable over a wide temperature range and in a variety of environments and produces signals compatible with standard electronic circuit designs. It is an object of this invention to provide such a hydrogen sensor.
It is another object to provide a hermetically sealed diffusion cell with a self-contained, long-lived ionization source.
A further object is the provision of means for allowing helium to diffuse out of the cell to thereby improve hydrogen sensitivity.
Another object is a hydrogen sensor cell formed only of inorganic material for operation in high temperature environments.